Resin compositions having desired conductivity by blending resin with conductive materials (e.g. carbon fibers) are known. Recently, various attempts have been made, such as increase in amount of blended conductive materials, use of particular conductive materials, combination of several conductive materials and the like, to achieve higher conductivity.
The increase in amount of blended conductive materials to achieve higher conductivity, however, gave rise to some problems in many cases such as high viscosity of the composition, large curtailment of mechanical properties, such as impact strength, deterioration of outer surface appearance of the molded products and the like.
One example of the use of particular conductive materials is blending resin with vapor grown carbon fiber, a nanotube and the like. Such technologies were disclosed in, for example, Japanese Patent Laid-open No. (Hei) 7-102112 and WO-2000-050514. However, these particular conductive materials are very expensive. Furthermore, considerable amount of these materials must be blended to achieve high conductivity with these materials alone. Accordingly, the price of the resin composition becomes expensive.
One example of the combination of several conductive materials is to combine carbon black with conductive fiber. Such technologies were disclosed in, for example, U.S. Pat. No. 4,604,413 and Japanese Patent Laid-open No. (Hei) 6-240049. These technologies can increase conductivity of conventional resin to some degree but deteriorates moldability (for example, flowability when molding) and mechanical properties. Therefore, they could not satisfy high conductivity and moldability simultaneously.
Another example of the combination of several conductive materials is to combine carbon fiber with particular small diameter carbon fiber (e.g. vapor grown carbon fiber). Such technologies were disclosed in, for example, U.S. Pat. No. 5,643,502 and Japanese Patent Laid-open No. 2000-44815. According to the above publications, however, it was found that some resin compositions having certain ratio of carbon fiber and small diameter carbon fiber does not increase conductivity and, in some cases, even lowers conductivity. Thus, it is clear that the above technologies cannot give good results.
Carbon fiber reinforced resin compositions are frequently used for various member of electronic devices, such as personal computers, office automation devices, AV devices, mobile phones, telephones, facsimile machines, household appliances, toys and the like because of their high shielding property against electromagnetic waves and good mechanical properties. Recently, with the development of portable devices, the thickness of the casing as well as the inner parts of the devices have to be small, which results in strong requirements for conductivity, mechanical properties, and moldability. Therefore, deterioration of such characteristic features becomes critical.
Given the above technologies, it was impossible to prepare carbon fiber reinforced resin composition, molding compounds and molded products therefrom that had high conductivity, show high shielding property against electromagnetic waves and satisfy moldability such as flowability when molding and ease of molding.
Purpose of the Invention
The present invention is intended to provide carbon fiber reinforced resin compositions, molding compounds and molded products therefrom, having good conductivity, mechanical properties and moldability, beyond the above conventional technologies.
Disclosure of the Invention
The present invention is based on investigation to solve problems in conventional technologies and the finding that carbon fiber reinforced resin compositions made by blending carbon fiber with particular small diameter carbon fiber in a specific ratio produces good results.
The carbon fiber reinforced resin compositions of the present invention have the following essential components:
Component (A): 0.01 to 0.7% by weight of vapor grown carbon fiber and/or nanotubes based on 100% by weight of the carbon fiber reinforced resin composition, of which the average diameter of single fiber ranges from 1 to 45 nm;
Component (B): 6 to 40% by weight of carbon fiber based on 100% by weight of the carbon fiber reinforced resin composition, of which the average diameter of single fiber ranges from 1 to 20 μm; and
Component (C): resin.
The molding compounds and the molded products of the present invention are characterized in that they are made by processing and molding said carbon fiber reinforced resin composition.